This invention relates to a method for monitoring the levels of chemical marker compounds and an assay kit enabling the monitoring to be carried out under field or laboratory conditions. The invention is particularly, but not exclusively, directed towards the detection of added chemicals in liquid products, especially in oil based products such as petroleum.
Chemical additives are important constituents of oil based products such as petroleum, diesel oil and lubricating oils. The additives are generally designed to impart favourable and occasionally unique properties to the product such that their absence or a reduction in their concentration may result in a significant loss of performance. These additives are normally introduced at a central distribution point into products which may be distributed on a world wide basis. Since product performance is dependent on the presence of appropriate levels of the additives in the final product as it is retailed, a system for demonstrating their presence at any point in the distribution chain is required.
A second, but equally important consideration, relates to the problem of counterfeiting. Products which are perceived to have favourable properties over rival products will be imitated for reasons of commercial gain. They may not, for example, enjoy the benefits of the correct additives but may be sold as to imitate visually the better product. In such a situation, the ability to distinguish the genuine product from imitations is highly desirable.
Accurate identification of oil based products is also important since litigation can be brought as a consequence of accidents and spillages. In these situations, the presence of a marker substance which can identify or alternatively exclude a particular manufacturer or distributor can be of extreme value.
In summary, the presence of readily identifiable marker substances in oil based products could contribute significantly to several aspects of quality assurance in the oil and petroleum industry. Up to now, it appears that no simple procedure has yet been devised to provide such a system.
Fuel additives are frequently beneficial to the performance of the product at extremely low concentrations. However, their incorporation into fuels at such low concentrations means that they are not readily detected by conventional analytical procedures. Even in situations where the additive can be detected by sophisticated physical/chemical techniques, there is the problem that samples must be taken to a central laboratory for analysis which may be tedious and time consuming.
One recent approach has been to make use of the fact that many organic compounds are immunogenic so that immunological assay methods can be applied to their detection (see for example EP-A-0327163). Though these methods do possess inherently high sensitivities, they are not intrinsically simple to perform and therefore do not lend themselves to analysis in the field. Moreover, they involve the use of monoclonal antibodies which may lack the stability of simple chemicals, again restricting the site or scope of application. This approach relies on subjecting a small sample to an assay procedure to quantify the additive compound of interest; there is no suggestion of introducing a chemical marker to the bulk product or along the distribution chain at source which is subsequently triggered possibly many weeks later several steps down the distribution chain to allow analysis or detection thereof.
We have developed a radically different approach which uses an independent substance which has some unique, easily detected property and which can be added to the fuel at source or along the distribution chain as a marker along with the additives. The marker should possess certain characteristics. Firstly, it should partition into the organic phase so that contact with water, as might occur for example in a storage vessel, will not cause substantial partitioning into the aqueous phase. Secondly, the marker compound should remain stable in the fuel for several weeks without substantial alteration of its detection characteristics. Thirdly, the marker compound should be reproducibly detectable at extremely low concentrations, partly for reasons of cost but also to ensure that it does not itself interfere with the performance of the fuel. The marker compound should be detectable quantitatively with a simple detection system. Finally, neither the fuel itself or any other additive should interfere significantly with the behaviour of the marker under normal analytical conditions.